Typically, match head compositions contain a major proportion by weight of potassium chlorate in admixture with a proportion of combustible material, e.g. starch, sulphur, charcoal or phosophorus sesquisulphide; a binder; an inert filler e.g. ground glass, zinc oxide, calcium sulphate, felspar, diatomaceous earth or china clay; and minor ingredients such as a burning rate catalyst, potassium dichromate, a dye or colourant, and/or a disperant. On a percentage basis (dry weight) a typical composition may contain
______________________________________ Potassium chlorate 35-65% Combustibles 5-20% Binder 7-20% Filler 20-33% Colourant 0-1% Catalyst 0-1% Dispersant 0-1% ______________________________________
In the case of strike-anywhere matches a significant proportion of the combustible material is provided by potassium sesquisulphide, whereas a typical safety match will contain a high proportion of potassium chlorate.
As the binder animal glues are extensively used, although other binders e.g. casein, albumen, alkyl vinyl ether/maleic anhydride copolymers, epoxy resins, polyvinyl acetate, polyvinyl alcohol, have been suggested from time to time. As match head compositions are usually applied to the match by dipping in an aqueous slurry or paste of the match head ingredients, a prime requirement of the binder is water-solubility or water-dispersibility. Also, since it is usual to incorporate into the match head a substantial quantity of air for the purpose of providing sensitivity a secondary requirement is for a binder of high foamability so that a slurry can be formed containing a high proportion of air bubbles which become incorporated into the match head. Also, of course, the binder must provide for the integrity of the head at all stages of storage, striking, ignition and combustion. Desirably also the binder is a combustible material. Although such criteria are met to a greater or lesser extent by the alternative binders mentioned, animal glue remains the binder of choice. Nevertheless animal glue possesses one major disadvantage, namely sensitivity to moisture, so that matches made therewith do not perform or store well in humid, e.g., tropical climates.
Various alternatives have been tried in order to provide a humidity resistant match head composition, including variations in the binder itself, and the provision of waterproof, e.g. shellac, coatings on the formed match head.
Typical prior art proposals for the production of humidity resistant matches are:
GB-A No. 2 098 975 which discloses humidity resistant matches comprising a conventional mixture of gelatin glue, sulphur, chlorate and conventional fillers to which has been added a proportion of an emulsified oil, e.g. linseed oil or liquid paraffin together with a proportion of hollow microspheres of a thermoplastic copolymer. Additionally, the binder in such compositions may contain 0-4% by weight of a water insoluble acrylate coploymer to increase the cohesion of the tip, such copolymer being added to the mix as an aqueous dispersion. The particular acrylate resins used in accordance with that proposal are not further identified.
Acrylate resins, more specifically acrylate ester copolymer resins, are also added to match head compositions in accordance with the teachings of FR-A No. 2 236 817 to provide humidity resistance.
Other additives providing humidity resistance in match head compositions are hollow ceramic micropheres (G.B.-B No. 1 506 185), epichlorohydrin or urea-formaldehyde resins (FR-B No. 1 515 152), polysulphides or epoxypolysulphide resins (GB No. 1 529 096), vinyl acetate (JP-A No. 74 92,209), casenite, viz a combination of casein and lime (JP-A No. 82 34,097), and various polymeric components inter alia methacrylate esters and glycerol chlorohydrin (U.S. Pat. No. 3 314 904), methyl vinyl ether/maleic anhydride copolymer (U.S. Pat. No. 3 441 456) and alkyl acrylate/catalyst combinations (Chem. Abs. 75, 152 504d, 1971).
An alternative approach has been to provide the finished match head with humidity resistant coating e.g. of cellulose acetate and chlorinated hydrocarbon (JP-A No. 74 47,510), methyl methacrylate/vinyl acetate copolymer (JP-A No. 75 04,222), shellac or notrocellulose (JP-A No. 78 62,813.
Despite all such proposals, the need still remains for an effective humidity resistant match head composition, and the present invention seeks to fulfil that need.